This invention relates to the production of glass fibers and more particularly to the production of glass fibers employing an orifice plate having closely spaced orifices.
The production of glass fibers employing an orifice plate having closely spaced orifices is described in detail in Strickland U.S. Pat. No. 3,905,790. According to the method therein described, the orifice plate with orifice plate heating means and closely spaced orifices is employed in conjunction with a bulk flow of rapidly moving gas, preferably air, directed upwardly at the orifice area in the plate. The bulk flow of gas, which is a generally single column of gas at the cone and plate area, is employed in an amount, velocity and angle sufficient to cool the cones to provide stable cone formation and maintain separation of cones. The bulk flow of gas impinges on the plate essentially to eliminate stagnant gas adjacent the plate and flows outwardly along the orifice plate in all directions. The bulk flow of gas also provides a supply of gas to be sucked downwardly by the fibers which are drawn from the cones of molten glass which form beneath the orifices of the orifice plate.
As U.S. Pat. No. 3,905,790 indicates, start-up may be achieved by allowing the underside of the orifice plate to flood, establishing the temperature of the orifice plate at from about 25.degree. C. to about 150.degree. C. below normal operating temperatures to restrict the flow of further glass through the orifice plate, and slowly withdrawing the matrix or monolith of glass which is formed beneath the orifice plate. As the monolith is slowly withdrawn, individual fiber-forming cones will tend to form at each orifice. The temperature of the orifice plate is then increased and the attenuation rate of the fiber is correspondingly increased with cone separation being maintained by the bulk air flow. This method is satisfactory but may require very careful operator attention, particularly with orifice plates having a larger number of orifices.
It is an object of this invention to provide an improved method of start-up for a heated orifice plate having closely spaced orifices that permits the running mode to be established in a short period of time.
It is another object of this invention to provide an improved method of clearing flooding of a heated orifice plate having closely spaced orifices that permits a rapid clearing of the flooded orifice plate.
It is a further object of this invention to provide a method of providing bulk gas flow for a heated orifice plate having closely spaced orifices that minimizes the volume of gas that is required.
It is yet another object of this invention to provide apparatus for start-up or for clearing flooding of a heated orifice plate having closely spaced orifices employing a gas delivery manifold that permits the running mode to be established in a short period of time.
It is still further an object of this invention to provide an apparatus for producing glass fibers from a heated orifice plate having closely spaced orifices employing a gas delivery manifold that minimizes the volume of gas that is required.
It is a still further object of this invention to provide a gas delivery manifold which may be employed both for clearing an orifice plate and for the production of glass fibers.
In one embodiment, this invention contemplates the method of establishing the running mode (i.e., either start-up or correction of flooding) of a glass fiber producing orifice plate having orifice plate heating means and closely spaced orifices comprising:
(a) Permitting molten glass to flood the underside of the orifice plate;
(b) Establishing the temperature of the orifice plate to provide a glass viscosity at the orifices of more than about 1000 poises;
(c) Forming a matrix of glass on the underside of the orifice plate;
(d) Directing cooling gas to the underside of said orifice plate from at least two sides of the orifice area at an angle of from about 30.degree. to about 60.degree. to said orifice plate from a plurality of generally opposed nozzles located closely adjacent said orifice area and which are directed generally to the center of the plate;
(e) Slowly withdrawing said matrix of glass from said orifice plate while increasing the temperature of said orifice plate and regulating the flow of said cooling gas to form fiber-forming cones under at least some of the orifices in said orifice plate; and
(f) Slowly decreasing and increasing the flow of cooling gas, said decreases in gas flow being sufficient to permit isolated flooded areas to flow to adjacent fiber-forming cones and said increases in gas flow being sufficient to increase the viscosity of the glass to cause flooded areas to fiberize as fibers are drawn from adjacent fiber-forming cones.
In another embodiment of this invention generally opposed nozzles are employed to maintain the running mode. Such embodiment is directed to a method of forming glass fibers by
(a) passing separate streams of molten glass through an orifice plate having orifice plate heating means and having at least four rows of orifices therein, with orifices being spaced in flooding relationship;
(b) drawing fibers from cones of molten glass formed at each said orifice; and
(c) directing a bulk flow of rapidly moving gas upwardly to the orifice area in said plate,
(i) to cool said cones to provide a stable cone formation and to maintain separation of cones thus preventing flooding; PA1 (ii) to impinge on said plate essentially to eliminate stagnant gas adjacent said plate and to cause gas to move outwardly along said plate in all directions from said orifice area; and PA1 (iii) to supply a source of gas sucked downwardly by the fibers and substantially eliminate ambient gas drawn into the region of the fiber cones,
and contemplates the improvement comprising introducing cooling gas streams from at least two sides of said orifice area through generally opposed nozzles which impact below but closely adjacent to said orifice plate and create a turbulent bulk flow of upwardly moving gas at the cone and plate area.
An additional embodiment of this invention contemplates the use of generally opposed nozzles to establish the running mode and thereafter employing generally opposed nozzles to maintain the running mode.
Still further embodiments of the invention contemplate an apparatus for establishing the running mode including generally opposed nozzles directed generally to the center of the orifice area; an apparatus for maintaining the running mode including generally opposed nozzles directed to impact below the orifice plate and provide a turbulent flow of upwardly directed bulk air; and an apparatus including generally opposed nozzles which may be altered from the clearing position to the running position.
This invention provides a method and apparatus which may be used for the successful clearing of orifice plates having closely spaced orifices even though the orifice plate may contain a large number of orifices. It has been determined that the practice of this invention reduces the volume of cooling gas required as contrasted with nozzles mounted more vertically beneath the orifice plate. Moreover, the use of the method described herein permits clearing more expeditiously than with the use of more vertically mounted nozzles since the cooling gas has better access to the orifice plate as the monolith is pulled away.
This invention also provides a method and apparatus which utilizes a bulk flow of cooling gas to maintain the running mode of a glass fiber producing orifice plate having closely spaced orifices which minimizes the volume of cooling gas that is required.
The various embodiments of this invention are improvements in the production of glass fibers as described in U.S. Pat. No. 3,905,790.
Broadly, the method described in U.S. Pat. No. 3,905,790 may be practiced with any glass melting means including conventional glass furnaces and auxiliary equipment. The molten glass is maintained in a reservoir which is in communication with the orifice plate. Most often, the orifice plate will form the lower surface of the molten glass reservoir means and, indeed, the orifice plate can be formed as a bushing with the sides of the bushing extending upwardly into the furnace to form all or a portion of the sides of the reservoir which contains the molten glass.
The orifice plate itself may be made of any alloy acceptable for operation under glass fiber forming conditions and the surface of the orifice plate is generally flat. The orifices in the orifice plate are most often less than about 0.1 in. in diameter and may be as small as 0.02 in. in diameter. In order to obtain maximum utilization of bushing area, the orifices generally are spaced not more than about 2 diameters center:to:center, with spacings of about 1.25 to about 1.7 diameters, center:to:center, being preferred. For practical production, orifice density generally will be at least about 50 orifices per sq. in., preferably at least about 100 orifices per sq. in., and most desirably about 200 orifices per sq. in. of the orifice area in the orifice plate. The orifice plates have at least four rows of orifices. preferably have at least about 10 or 11 rows of orifices, and most desirably have at least about 15 rows of orifices. The orifice plate configurations and assemblies described in copending applications Ser. No. 599,720 filed July 28, 1975 and Ser. No. 638,526, entitled Apparatus and Method for Controlling Flooding in the Drawing of Glass filed Dec. 8, 1975 are particularly suitable for use.
While a variety of cooling gases may be employed, air is particularly preferred. Since the gas is employed for cooling purposes it is preferred to employ gases having temperatures of about ambient temperature (e.g., about 100.degree. F. or less). The benefits can also be achieved by warmer gas which may be, for example, even at 500.degree. F., providing the volume of gas is increased accordingly. For ease of presentation, this discussion will be couched in terms of air but it should be understood that other gases are also contemplated.
The orifice plate is equipped with orifice plates heating means so that the temperature of the orifice plate can be regulated independently of the heat transferred to the orifice plate from the molten glass. Most often such heating means are electrical resistance heating means although other means are also contemplated.
The fibers are drawn from the fiber forming cones on a collet, or the like, and may be coated with conventional dressing fluids, sizing compounds and the like. The method to which this invention is directed is fully discussed in U.S. Pat. No. 3,905,790, which is incorporated herein by reference, and that discussion will not be repeated at length here.
One of the essential means for achieving the above and other objects of this invention is the provision of an auxiliary gas cooling system for use in establishing the desired running mode of flat orifice plate bushings. This gas cooling system is auxiliary in the sense that it is in addition to, and desirably not in lieu of, the bulk air system which flows in a generally upward fashion to cool the flat orifice plate and the attenuated filaments moving downward in the conventional operation of the process embodied in U.S. Pat. No. 3,905,790. The auxiliary system in effect is a multiple air lance that expedites the establishment of the normal running mode of the bushing, either at start up or after a breakout during the course of a run. The method of the invention contemplates several air nozzles disposed at opposite sides along the length of the bushing and at the angles heretofore noted. The center line of the gas flowing from each nozzle exerts a cooling effect on the orifice plate as the matrix of glass drops or flows away from the plate face as flooding is being curtailed and terminated, all in the manner more fully described herein, and the jets of gas flow upwardly and in toward the center of the orifice plate. The multiplicity of nozzles projecting individual jets provide the multiple air lance effect heretofore noted. The air, or any other gas, can be directed at random along the length of the orifice plate to maintain a uniform temperature and cooling effect along the length of the plate. The invention is particularly useful for large bushings, that is, bushings in excess of 1000 orifices. For example, in bushings of 2000 orifices or more which are rectangular in shape and wherein there is a relatively long dimension at the ends of which the current is fed to effect the heating of the bushing, such as is shown in the bushing assembly of FIG. 3 of the aforementioned Ser. No. 638,526, the ends of the orifice plate adjacent the current leads may in some instances be at a higher temperature than the midsection of the orifice plate. The nozzles can be readily adjusted to apply a greater cooling effect to the hotter ends to evenly cool the orifice plate along its length.
This auxiliary cooling system with its multiple air lance effect furnishes distinct advantages in starting up or clearing breakouts, particularly where substantial flooding is permitted to take place in the first instance, in that the time of the operator is substantially reduced in contrast to the time and cost for a single operator or multiple operators to clear the bushing manually with individual air lances. As the size of bushings increases, so also do the advantages flowing from the use of the multiple air lance. In fact, in some instances the need for an operator can be obviated entirely.
It is emphasized that the concept of opposing jets, particularly when intended to impact directly on the orifice plate of the bushing, constitutes a most advantageous embodiment of this invention when employed to establish the running mode of the bushing on start up or after a major flood where an extensive matrix of glass has been permitted to form. Nevertheless, very useful results can also be obtained in another embodiment of the invention as elsewhere described, where the center lines of opposing jets are permitted to impact against each other ahead of and before they reach the orifice plate. The effect of the impacting jets is to create an upward air flow onto the orifice plate.
Generally, where the jets of the auxiliary cooling system impact directly on the orifice plate and the running mode is established, the upward flow of bulk air is continued and the flow from the auxiliary system is terminated. However, the operator can continue the auxiliary flow if desirable.
In the embodiment of the invention involving impacting jets ahead of the orifice plate, it is possible to use the system, depending on the volume of air flow, to assist in establishing the running mode of the bushing. Also, if desired, it can be used as the source of bulk air flow or to augment the conventional bulk air flow of the process of U.S. Pat. No. 3,905,790.
In respect of the direction of air flow it is to be noted that in establishing the running mode of the bushing utilizing the multiple air lance effect of the auxiliary cooling system it is generally preferred to direct the opposing air nozzles so that the principal force of the respective jets is felt at the outer edges of the orifice plate and consequently the flooding effect giving rise to the matrix of glass tends to flow inward toward the center of the orifice plate. It is more desirable to concentrate the matrix in this manner where its weight is relied upon, at least in part, to encourage filament attenuation.
Although the angle of the opposing jets to the orifice plate has been discussed elsewhere, it is pertinent to note that the range of the angles can vary from about 30.degree. to about 60.degree.. Below about 30.degree. the air tends to blow by and not impact on the plate or if impacting with an opposing jet the air will not have a sufficient upward moment to provide an effective upward flow. However, in the case of impacting jets, when one of the opposing jets is set as low as about 30.degree. the immediate opposing jet should be at a greater angle. Also, it is desired practice that the nozzles from which the jets at the lower angles approaching about 30.degree. are ejected should be on the same side as the operator so that the flow of heated air and gas from the vicinity of the orifice plate area after contact is away from the direction of the operator.
Another advantage of the auxiliary air cooling system, particularly the impacting jets, is that it aids in line drying of the fibers that may have been sprayed with cooling water.